266 ABSORPTION LYMPH AND CHYLE 



The general rapidity of the current in the lymphatic vessels has never 

 been accurately estimated. As a natural consequence of the variations 

 in the distention of these vessels, the rapidity of the circulation must 

 be subject to frequent modifications. It has been calculated that the 

 rapidity of the flow in the thoracic duct is about one inch (25.4 milli- 

 meters) per second. This estimate, however, can be only approximate ; 

 and it is evident that the flow must be much less rapid in vessels near 

 the periphery than in the large trunks, as the liquid moves in a space 

 that rapidly becomes contracted as it approaches the openings into the 

 venous system. 



Various influences combine to produce the movements of liquids in 

 the lymphatic system, some being constant in their operation, and others, 

 intermittent or occasional. These will be considered, as nearly as pos- 

 sible, in the order of their relative importance. 



The forces of osmosis and transudation are undoubtedly the main 

 causes of the lymphatic circulation, more or less modified, however, by 

 influences that may accelerate or retard the current ; but this action is 

 capable in itself of producing the regular movement of the lymph and 

 chyle. It is a force that is in constant operation, as is seen in cases of 

 ligation of the thoracic duct, a procedure which must finally abolish all 

 other forces that aid in producing the lymphatic circulation. When 

 the receptaculum chyli is ruptured as a consequence of obstruction of 

 the thoracic duct, the vessel gives way as the result of the constant 

 osmotic action, in the same way that the exposed membranes of an 

 egg may be ruptured when immersed in water. 



The situations in which the osmotic force originates are at the 

 periphery, where the single wall of the vessels is thin, and where the 

 extent of absorbing surface is large. If liquids can penetrate with such 

 rapidity and force through the walls of the bloodvessels, where their 

 entrance is opposed by the pressure of liquid already in their interior, 

 they certainly must pass without difficulty through the walls of the 

 lymphatics, where there is no lateral pressure to oppose their entrance, 

 except that produced by the weight of the column of liquid. This 

 pressure is readily overcome ; and the valves in the lymphatic system 

 effectually prevent any backward current. 



In describing the anatomy of the lymphatic system, it has already 

 been stated that the large vessels and those of medium size are provided 

 with non-striated muscular fibres and are contractile. This has been 

 demonstrated by physiological as well as anatomical investigations ; and 

 it is not uncommon to see the lacteals become reduced in size to mere 

 threads, even while under observation. Although experiments usually 

 have failed to demonstrate any rhythmical contractions in the lymphatic 



